Enable Linked Mailbox Error: The user account "domain\username1" to be linked has already been the master account of another linked mailbox (150355)

Title

Enable Linked Mailbox Error: The user account "domain\username1" to be linked has already been the master account of another linked mailbox

Description

Getting an error below when mailbox enabled for linked mailbox:

11:52:46 ERROR: [7437-1-193-00000000]Unable to enable object. Reason: 'Enable Linked Mailbox Error: The user account "domain\username1" to be linked has already been the master account of another linked mailbox "domain.com/MailUsers/username2". Choose a different user account.

Cause

The issue is due to the Mail User object was already linked to another mailbox.

Resolution

To check if the Mail User object was already linked to another mailbox, please follow the steps below:

- Open up the Exchange Powershell cmdlet as Administrator
- Run this command "Get-User -Identity “domain\username1” | FL LinkedMasterAccount"

NOTE: Make sure that the LinkedMasterAccount properties value is null.